I combined several small changes into one patch here. I believe I
started by noticing that the "title" is not needed by tui_gen_win_info
and could be self-managing (i.e. std::string). Moving this revealed
that "can_box" is also a property of tui_win_info and not
tui_gen_win_info; and this in turn caused the changes to
tui_make_window and box_win.